To take this a little further, HighPlains' post is very informative but he missed one little detail that most don't think about. When he said lowering the nitro is like richening the needle, he is 100% correct. The reason for this is that when you add nitro, you remove fuel from the mix. Nitro is an oxidizer, meaning it adds additional oxygen to the combustion process. The effect is like turbocharging a car engine, more oxygen=more power, but at a price. To make use of the additional oxygen, you need more fuel to go with it. Not having enough fuel results in running lean, subjecting the engine to early detonation and higher than optimum heat levels. In your full sized car, this would sound like "knocking". This, just like in a nitro motor, robs power and damages parts. Since I run 50% nitro in my boats, the effect is even more pronounced. I have a marine .67 engine that has a badly pitted head and piston due to detonation, caused by a different issue. Regardless, the general rule of thumb is when you increase nitro, you richen the needles